Synchronous Buck Converter With Output Impedance Correction Circuit

Abstract

This study is related to the improvement of the output impedance of the buck converter by means of introducing an additional power path that virtually increases the output capacitance during transients. It is well known that in voltage regulation module applications, with wide load steps, voltage overshoots and undershoots may lead to undesired performance of the load. To solve this problem, high-bandwidth high-switching-frequency power converters can be applied to reduce the transient time or a big output capacitor can be applied to reduce the output impedance. The first solution can degrade the efficiency by increasing switching losses of the MOSFETS, and the second solution is penalizing the cost and size of the output filter. The output impedance correction circuit, as presented here, is used to inject or extract a current n-1 times larger than the output capacitor current, thus virtually increasing n times the value of the output capacitance during the transients. This feature allows the usage of a low-frequency buck converter with smaller capacitor but satisfying the dynamic requirements.